Can anyone help w/my electrical prob.

I have an 85 K5 350 cid. with A/C. Every time I turn on the A/C the volts go down into the red and if I try to use the power windows the volts go down even more. Some times the windows will stop. At a stop light I have to turn of the A/C in fear. I have talked to shops and people and they have no idea. So I am asking the good people here to find an answer.
Thanks,
BlueOx

First thing to check is the ground strap off the back of the passenger side head to the fire wall. It is often forgotten when the engine is removed and it is the main ground for the body. The ground to the engine from the battery should be good since it starts. The next possible problem is that somewhere along the way a 37 amp alternator got put on the truck. You truck is supose to have a 65 amp alternator or better. If you have a VOM then you can check the voltage in the truck compaired to the voltage at the battery. Mesure the battery voltage before starting the truck. If you have a 13-14.5 volts at the battery but in the truck your showing a big drop then you have either lost the ground as I described or the main power feed into the cab is bad. Thats the thick red wire on the fire wall that hits the terminal deal above and to the right of the distributor. It picks up it's power at the starter.

Maybe your alternater is bad or going bad. When your truck is running, that is what powers everything. I guess you could even have the wrong alternater on your engine....one that cant handle the load you are dishin it????
Anyways, just a thought, maybe something to check out.
Good luck!

I type so slow, by the time I sent in my reply for this one, there where already 3 replies there which weren't there when I started typing. Just reading down it all, kinda makes me sound like an idiot, just repeating what yall said........heheh.
oh, well

The other posts are good, but since it only happens when your AC is on(right), it may have something to do with the AC wiring. Such as a bad ground on the AC pump? I know the pump has an electric clutch on that which may? draw some significant juice it all the contacts aren't good. This would possibly be fixed by Grim's suggestion of checking the ground strap.

First off....everything runs off the BATTERY. The alternator is there to keep the battery charged. The voltage regulator, built in to the alternator, watches the battery, when it's voltage falls below the set float voltage, it brings the alternater on line to bring the battery back up to just over the float voltage, and then it drops out of the loop. That is why they call it the voltage regulator. If it stayed on all the time it would continually overcharge the battery.

the problem I see is that possibly the regulator is failing and not keeping the battery at float voltage, as is present in the voltage readings you are getting. If you are handy...you can get rebuild parts for your alternator and save some bucks...

Well ideal voltage at the battery with the vehicle running at idle should be in the 13.5-14 volt range. With the AC and lights on you may see 13 volts at the battery at idle but once you come off idle to say 1200 rpm you should be up near 14 volts again. In the vehicle you will see about 13 volts due to loss between the battery and the cab. From your reading of under 11 volts my guess is problem in the alternator more than likely a open Diode in the regulator like somebody else mentioned.
If it were my truck I think I would get the life time 105 amp from Auto zone and be done with it. If it ever fails again they just hand you a new one. If you have a winch it will fail again You could rebuild it and get some life out of it but your not going to have the tools to turn the stator shaft and metering out the windings can be a pain in the butt and belive me $100 is sure worth it if you have ever rewound an armature by hand. If all your grounds and other connections between the Battery and the alternator are good then it sounds like just a bad alternator (regulator is built inside it).

I also think that it's your alternator, but here's something else to look into:

When the AC compressor is engaged, there is a little solenoid on the carbuerator throttle linkage that bumps the idle speed up a little bit. This is to keep the engine from bogging down with the load of the A/C on it. If that doesn't work right, your rpms may be too low for the alternator to work efficiently. Generally, though, you can supply a decent load down to 500-600 rpms, but for a heavy load, you may want to be up closer to 800 or 900 rpms, depending on your truck and your alternator. Even if this solenoid works right, you may want to adjust it or even adjust your normal idle speed up a little bit.

I mention this only as something to do once you get your normal operating voltage up. Unless you just started the truck 20 seconds ago, you should always be above 12.5 or 13 volts except maybe in gear, warm, with everything turned on. But even then, you shouldn't be below 12 or something is wrong. If your voltage never comes up, swap the alternator. If your battery is old, you might want to think about that, too. If your battery has a bad cell, it can require tons of current to keep the voltage up to the where the regulator wants it, and that spells short life for your alternator.

Autozone or a similar store will gladly test your battery and alternator for you for free. Here's another way to test them yourself. First, make sure that the electrical connections are good at the battery, the chassis, the block and the alternator. After driving for a little while at night, stop and aim the lights at a wall or something. Shut off the engine without turning the lights off. If the lights dim a little, that's fine. If the lights dim a lot, your battery needs to be replaced. Now, assuming that your battery is good: Measure the voltage on your battery terminals before starting the truck and make note of it. Then start the truck and watch what happens to the battery voltage. It should increase to at least 13 volts, probably more like 14. The voltage should continue to stay above 12.5 or 13 volts with the lights on, heater blower on high, etc. If it just keeps slowly dropping, you are draining the battery and the alternator is bad. If your battery is good and the voltage never comes up to the right level, that also means that the alternator is bad. For this test to be clearer, it may help to drain the battery a little bit before starting the engine by running the lights or something to get rid of the "pump-up" voltage that a recently charged battery will have.

Sorry that this is so poorly structured, but I hope that it helps.

85 pretending to be a 90
350 swapped in for stock 305
5" of suspension lift 33/12.5/16.5

I want to thank everyone that wrote in and helped. After all the wire chasing it truned out to be the alt.
I took it to Autozone to have it tested and the alt. was only putting out 1.7 amps. WOW! They didn't have the 105 amp. I got a 95 amp with a lifetime warranty for only $60. Is that good?

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